Water chemistry of the Zhujiang (Pearl River): Natural processes and anthropogenic influences

[1] The temporal and spatial variations of major ions in the Zhujiang ( Pearl River) were analyzed using long-term water chemistry data of major dissolved ions (Ca2+, Mg2+, the sum of Na+ and K+, HCO3-, SO42-, Cl-) and dissolved silica (SiO2) from 75 hydrological stations ( 1958 - 2002). The total dissolved solids (TDS) within the Zhujiang basin varies from 34.0 mg/l to 416.1 mg/l generally decreasing from upstream to downstream along the main stem of the Zhujiang. Rock weathering is the dominant controlling factor for the water chemistry of the Zhujiang, and more specifically, on average, 68% ( 22 - 92%) of total dissolved load comes from carbonate weathering, 22% ( 2 - 68%) from silicate weathering, and 10% ( 3 - 24%) from evaporite weathering, respectively. The flux calculations indicate that in total about 41.8 x 10(6) tonnes/year of TDS are transported out of the Zhujiang ( excluding the Delta Region), averaged for the period 1958 - 2002. Changes in water chemistry can be observed from long-term trend analysis, notably for SO42- and Cl-, as a result of anthropogenic influences, such as acid deposition, domestic and industrial wastewater discharge, and basin water resource development. An intense reforestation policy coupled with rapid reservoir development in the Zhujiang Basin would trigger more significant anthropogenic impacts on water chemistry in the future.